Cook the Pasta: Bring a large pot of salted water to a boil. Add the rotini pasta and cook according to package instructions until al dente. Drain and set aside.
Prepare the Chicken: In a large skillet over medium heat, add olive oil. Once hot, add the diced chicken breast. Season with salt, pepper, and Cajun seasoning. Cook until the chicken is golden brown and cooked through, about 6-8 minutes.
Sauté Garlic and Peppers: Add the minced garlic and diced red bell pepper to the skillet with the chicken. Sauté for an additional 2-3 minutes until fragrant and the pepper begins to soften.
Make the Sauce: Pour in the heavy cream and stir well, scraping the bottom of the skillet to combine all flavors. Bring to a simmer, then reduce the heat to low.
Add Cheeses: Stir in the shredded cheddar cheese and Parmesan cheese. Mix until the cheeses melt and the sauce is smooth. Adjust seasoning if necessary.
Combine: Add the cooked rotini to the cheese sauce and chicken mixture. Toss everything together until the pasta is evenly coated with the sauce.
Garnish and Serve: Once combined, remove from heat and let it sit for a few minutes. Serve hot, garnishing with chopped green onions for added freshness.